Process of coating pigments



Patented 1.... '19, 1931 rnocsss or COATING PIGMENTS William J. O'Brien, Shaker Heights, Ohio, as-

signor to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application 'June 14, 1932,

' Serial No. 617,248

V 6 (Cl. 134-58) Among the objects of this invention is the formation of a pigment which will yield a smooth and fine-grained film or coating when associated with ordinary liquid vehicles and spread as a surface coating.

A further object of this invention is the coating of pigment particles with a protective colloid whereby the properties of the pigment are modifiedand improved so that the pigment will form 10 a smooth, easy-working paint that is free from agglomerates. The pigments so coated tend to remain in suspension in the paint vehicle for a much longer period of time than pigments not so treated; Other, further and more specific objects of this invention will, become readily apparent to persons skilled in the art from a consideration of the following description.

-In the preparation of pigments by the methods heretofore employed, the resulting powdered pigment when incorporated with a vehicle, such as linseed-oil or other drying and semi-drying oil, yields a paint surface which frequently is not as smooth and fine-grained as desired, due to the existence of agglomerated particles of the pigment. This agglomeration persists to an undesirable extent despite the grinding of the pigment in oil. I have found that by adding suitable quantities of certain organic compounds (for example, oleic acid, stearic acid, palmitic acid, lauric acid and the sodium, potassium, magnesium, calcium and'ammonium salts of alginic acid) to a suspension of a pigment in water the tendency for the pigment particles to agglomerate is largely diminished, and when the pigment containing these organic compounds is ground in a vehicle asa paint, the paint film produced therefrom 1 is smoother and freer from grains or coarse par- 40 ticles and results in a very smooth paint job. The effects of additions of small quantities of these fatty acids to the pigment may be attributed to a change in the surface tension of the individual particles of pigment by the presence of 5 these .fatty acids so that, there is no longer any tendency for these particles to collect in clusters or -agglomerates. It appears that these organic compounds coat the particles of pigment, acting as protective colloids and change the surface ten- 5 sionof the particles so that theydo not ag- 'glomerate. The quantity of protective colloid employed in my special process may vary from 0.05% to 1% depending upon the-pigment and colloid employed. When employing oleic or 55 stearic acid as a colloid with a pigment such as zinc oxide, colloid material equal to 0.1% of the weight of the pigment has been found very satisfactory. The fatty acids which I have found suitable for this purpose are those which are solid at. ordinary 5 temperatures and contain not over 18 carbon atoms.

A specific example of carrying out this invention is as follows: To a warm, wet, slurry of zinc oxide in water there is added about 0.1%

oleic acid, and the mixture is thoroughly ground, whereupon itis filter-pressed to remove the water, then dried and later ground in dry form.

- The resulting pigment, after incorporation with In this system, the oil of the paint appears to constitute the external phase, the pigment forming the internal phaseand the oleic acid being the protective colloid.

The oleic acid or other suitable protective colloid material may be added either in molten 25 state or as a solution or emulsion in water. I have found a tube mill very satisfactory in producing a thorough incorporation of pigment and protective colloid.

My new process of treating the pigments is to 30 be clearly distinguished from the mere addition of stearic and oleic acids and certain salts of these acids to paints forthe purpose of prevent ing settling and giving body to the paint. My process is designed for a different purpose; name- 5 ly, the. alteration of the properties of the pigment itself which is brought about preliminary to the grinding of the pigment in oil. Furthermore, where heretofore the oleic and stearic acids and their salts have been added to paints, from 1 to 40 2% of the total weightof the paint including the vehicle is necessary to accomplish the desired effect in the paint. By my process of treating the pigments a very much smaller quantity of oleic and stearic acids will produce the totally different effect in the pigment-itself, for usually with oleic or stearic acid equal to 0.1% of the weight of the dry pigment I am able to cover the pigment with the requisite amount of protective colloid or deflocculating agent to yield a pigment possessing the new modified properties.

My process finds suitable application for the treatment of other pigments besides zinc oxide, examples of some other pigments being whiting,

white lead, 1ithopone,- iron reds, titanium pigments, blanc fixe, ground barytes, carbon black,

lamp black and other carbon pigmentsfetc.

I have also found that the beneficial 'eiifectsv of coating the pigments as above described also exist where the pigment so treated is used for purposes other than in paints; for example, as fillers in plastic compositions, rubber compositions and molded products. where the pigments are to be used in compositions that do not have oils or similar liquid vehicles as their components, the quantity of protective, colloid coating or agent may be increased to as much as 5% of the weight of pigment for most uses and to as much as 15% for special purposes.

The present invention is not limited to the specific details set forth in the foregoing examples which should be construed as illustrative and not by way of limitation, and in view of the numerous modifications which may be effected therein without departing from the spirit and scope of this organic acids and their salts consisting of stearic aooaoco acid, oleic acid, palmitic acid, lauric acid, and drying theresulting product.

2."I"he method of producing surface coated pigments which comprises suspending finely divided zinc oxide in water, incorporating from .05

v to 1% of a, substance selected from the group of aliphatic organic acids and their salts consisting of stearic acid, 'oleic acid, palmitic' acid, laurlcacid, and drying the resulting product.

3. The method of producing surface coated pigments which comprises suspending finely divided titanium pigments in water, incorporating from .05 to 1% of a substance selected from the group of aliphatic organic acids and their salts consisting of stearic acid, oleic acid, palmitic acid,

lauric acid, and drying the resulting product.

4. The method of producing surface coated pigmerit barium sulphate in water, incorporating from .05 to 1% of a substance selected from the group of aliphatic organic acids and their salts consisting of 'stearic acid, oleic acid, palmitic acid, lauric acid and drying the resulting product.

5. The method of producing surface coated pigments which comprises suspending finely'divided titanium pigment in water, incorporating from .05 to 1% of a salt of stearic acid, and drying the resulting product.

6. The method of producing surface coatedpigments which comprises suspending finely divided barium sulphate in water, incorporating from .05 to 1% of a salt of stearic acid, and drying the resulting product.

WILLIAM J. O'BRIEN.

s which comprises suspending fin'ely divided 

